They showed gravity wrinkled spacetime in just the way Albert Einstein predicted in his theory, published in 1915.

The neutron star is a rapidly spinning "pulsar" that acts like a lighthouse, emitting regular flashes of intense radio waves.

Made from the crushed inner core of a giant exploding star, it measures just 20 kilometres across but is so dense that a sugar cube-sized lump of its material would weigh more than a billion tonnes on Earth.

The pulsar's gravity is at least 300 billion times greater than the Earth's, causing a significant distortion in spacetime according to Einstein's theory. It is locked by gravity to a companion, a less dense white dwarf - the glowing remnant of another dead star that has shed its outer layers.

As they circle each other, the objects should emit gravitational waves - wrinkles moving out in spacetime - that lead to a loss of energy and cause them to move closer together. The effect can be measured on Earth by very precisely timing the arrival of the pulsar's radio bursts over a long period of time.

Astronomers writing in the journal Science said the results exactly matched the predictions of General Relativity, pushing Einstein's theory to new limits. "We thought this system might be extreme enough to show a breakdown in General Relativity, but instead, Einstein's predictions held up quite well," said Dr Paulo Freire, from the Max Planck Institute for Radioastronomy in Germany.

Alternatives to Einstein's theory would have required the binary system made up of the pulsar and white dwarf to lose energy much faster than was observed.

Co-author Professor Marten van Kerkwijk, from the University of Toronto in Canada, said: "The observations disprove these alternatives, and thus give further confidence that Einstein's theory is a good description of nature - even though we know it is not a complete one, given the unresolved inconsistencies with quantum mechanics."